274 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
EXPLANATION OF PLATES. 
PLATE LXXXVIII. 
Fig. 1. Section through oil globule of segmenting egg. 
Fig. 2. Surface view of a segmenting egg, two hlastomeres in which nuclear division has already 
taken place. 
Fig. 3. View from below of S-blastomere stage. 
Fig. 4. Irregular S-blastomere stage. 
Fig. 5. 8-blastomere stage of mackerel, radial division. 
Fig. 6. Blastoderm showing cellular division, 8 into 16. 
Fig. 7. 16 into 32 cells; opposite cells divide at same time. 
Fig. 8. Blastoderm showing normal cleavage, 16 into 32. 
Fig. 9. Stage of 16 into 32, variation. 
PLATE LXXXIX. 
Fig. 10. Stage of 16 into 32 — variation. 
Fig. 11. Resting blastoderm of 32 cells. 
Fig. 12. Blastoderm — 32 into 64. 
Fig. 13. Section through center of l-blastoraere stage. 
Fig, 14. Stage of 8 cells — section is through a of Fig. 3. 
Fig. 15. Stage of 8 cells — section is through 6 of Fig. 3. 
Fig. 16. Stage of 16 into 32 cells — section lies through a to 6 of Fig. 8. 
PLATE XC. 
Stage of 16 into 32 cells — section is through c to d of Fig. 8. 
Stage of 32 cells — lower cells just beginning to divide — through a~h of woodcut, Fig. 1, PI. 9. 
32 into 64 cells — through d-f of woodcut. Fig. 1. 
Section through late segmentation stage. 
Surface view of edge of blastoderm of 4.40 hours — marginal cells still distinct. 
Surface view of blastoderm edge— 7.30 hours — marginal cells not marked olf from the periblast. 
Surface view of blastoderm edge — 8.30 hours — outlines of marginal cells entirely lost. 
Surface view of blastoderm edge — 9.30 hours — multiplication of periblastic nuclei. 
PLATE XCI. 
Fig. 25. Section through blastoderm of about same stage as Fig. 22. D. 4. 
Fig. 26. Section through a blastoderm such as Fig. 23. D. 4. 
Fig. 27. Section through periblastic wall (about same stage as Fig. 24). D. 4. 
Fig. 28. Section through periblastic wall (about same stage as Fig. 24). D. 4. 
Fig. 29. Section through blastoderm (9.30 hours) of about same stage as Figs. 24, 27, 28. A. 4. 
Fig. 30. Section through blastoderm of 14 hours. A. 4. 
Fig. 31. Section through blastoderm of 16 hours. A. 4. 
Fig. 32. Surface view of blastoderm (16 hours) in which the “raudwulst” is just marked out at em- 
bryonic pole — first stage iu formation of germ ring. A. 4, 
Fig. 17. 
Fig. 18. 
Fig. 19. 
Fig. 20. 
Fig. 21. 
Fig. 22. 
Fig. 23. 
Fig. 24. 
